Dehydrogenation Of MgH2 Research Articles

Enhanced dehydrogenation of MgH2 modified by Ti and S: A first-principles investigation

The present work gives the structural, dehydriding and electronic characteristics of MgH2 with Ti or/and S additives by first-principles density functional theory calculations. It is found that Ti and S prefer to occupy Mg site and interstitial site, respectively, in terms of occupation energy (Eocc). Furthermore, Ti + S incorporation into MgH2 lattice is more energetically favorable (Eocc = −0.051 eV–0.944 eV) relative to single Ti incorporation (Eocc = 1.314 eV–1.784 eV), for which the promotion of adequate Mg site by S addition is chiefly responsible. Ti, S, and especially Ti + S doping not only reduce the hydrogen dissociation energy from 1.619 eV/2.317 eV (Mg16H32) to 0.350 eV/0.967 eV (Mg15TiSH32) for H-atom/H-molecule desorption, but also decrease the hydrogen diffusion energy barrier from 0.706 eV/0.704 eV (Mg16H32) to 0.342 eV/0.169 eV (Mg15TiSH32) along path I/II, respectively. As a result, a significant improvement on the thermodynamical and kinetical performance of MgH2 can be achieved using Ti or/and S. This improvement is attributed to the higher electronegativity of Ti (relative to Mg), the decrease of Mg–H interaction and the formation of Ti–H and Mg–S bonds. Our studies provide new insight into the enhanced dehydrogenation of MgH2 modified by Ti and S, which is useful for designing advanced magnesium hydrides with favorable H-desorption performance.

Modification research on the hydrogen storage performance of bimetallic oxide Zn2Ti3O8 on MgH2

In this study, flake Zn2Ti3O8, TiO2 and rod ZnO catalysts were successfully synthesized by hydrothermal and calcination methods, and the catalytic performance of the three catalysts for MgH2 was compared. Notably, Zn2Ti3O8 had a significant synergistic enhancement effect on the dehydrogenation temperature and desorption kinetics of MgH2. The experimental results showed that the dehydrogenation of MgH2 + 12 wt% Zn2Ti3O8 composite started at about 195 °C, which was about 150 °C lower than that of pure MgH2. Moreover, at 325 °C, MgH2 released only 3.06 wt% H2 in 20 min, whereas the MgH2 + 12 wt% Zn2Ti3O8 composite released the same amount of hydrogen at 250 °C in 3 min. After complete dehydrogenation, the MgH2 + 12 wt% Zn2Ti3O8 composite initiated hydrogen uptake at 40 °C and absorbed about 6.05 wt% of H2 in 60 min at 200 °C. The hydrogen uptake activation energy and dehydrogenation activation energy of the composites were reduced by 24.56 kJ/mol and 44.67 kJ/mol, respectively, when compared to the pure MgH2. Cycling experiments showed that after 20 cycles, the MgH2 + 12 wt% Zn2Ti3O8 composite maintained good cycling stability and the hydrogen storage capacity was still more than 96 %. Therefore, the composite exhibits excellent catalytic and hydrogen storage properties, and has potential applications in improving the hydrogen release rate and reducing the activation energy.

Unraveling the kinetic mechanism of atomic hybrids for the catalytic dehydrogenation of MgH2

Herein, we report the multi-metal atomic catalysts for solid-state dehydrogenation of MgH2. It aims to reveal the multi-element synergy in catalysts for solid-state hydrogen storage. The kinetic measurements and fitting reveal two mechanisms: one shows a maximum rate at the early stage, such as V and Cr; the other needs a temperature-sensitive preparation time for its maximum rate, such as Ni. The combination of two catalyst components demonstrates the best kinetics: V and Cr boost the initial dehydrogenation, and Ni benefits the further hydrogen transfer which alleviates the rate of decay. This work provides guidelines for the design of multi-element doped catalysts for MgH2 dehydrogenation.

Modification of MgH2 hydrogen storage performance by nickel-based composite catalyst Ni/NiO

In this study, the Ni/NiO catalyst was demonstrated to enhance the hydrogen storage performance of MgH2. The dehydrogenation of MgH2+10 wt% Ni/NiO started at approximately 180 °C, achieving 5.83 wt% of dehydrogenation within 10 min at 300 °C. Completely dehydrogenated, MgH2 began to rehydrogenate at about 50 °C, absorbing about 4.56 wt% of hydrogen in 10 min at 150 °C. In addition, the activation energies of dehydrogenation and rehydrogenation of MgH2+10 wt% Ni/NiO were 87.21 and 34.84 kJ/mol. During the dehydrogenation/rehydrogenation cycle, Mg2Ni/Mg2NiH4 could promote hydrogen diffusion, thus enhancing the hydrogen storage performance of Mg/MgH2.

Amorphous mixed transition metal oxides: A novel catalyst for boosting dehydrogenation of MgH2

Magnesium hydride (MgH2) has been recognized as a promising hydrogen storage material. However, the sluggish hydrogen desorption kinetics is one of the main factors hindering its practical applications. To enhance the dehydrogenation kinetics of MgH2, an amorphous mixed TiO2-ZrO2-V2O5 catalyst is synthesized in this work. After adding the as-synthesized catalyst into MgH2 by ball milling, the dehydrogenation activation energy can be decreased to 65.7 kJ mol−1. Meanwhile, the catalyzed MgH2 shows excellent cycling stability after fifty hydrogen absorption-desorption cycles. The significant improvement of hydrogen desorption kinetics is attributed to the synergistic effect of abundant oxygen vacancies and in situ formed multivalent species in the catalyst. This highlights the importance of designing and synthesizing efficient catalysts for dehydrogenation of MgH2.

Heteroatom sulfur exploration for enhancing MgH2 dehydrogenation: A theoretical and experimental analysis

High operating temperatures and sluggish kinetics constrain the commercial application of magnesium-based hydrogen storage materials. To overcome these drawbacks, this work investigates heteroatom sulfur as a catalyst to improve the dehydrogenation of MgH2 using density functional theory (DFT) and experimental validation. Heteroatom sulfur can influence the dehydrogenation of MgH2 by modulating interfacial carbon-magnesium interactions and substituting surface hydrogen sites. In particular, DFT calculations reveal that sulfur functional groups facilitate charge transfer and significantly reduce the energy barrier of MgH2 by 0.32 eV–1.59 eV. Substitution of sulfur atoms at surface hydrogen sites of MgH2 notably improves dehydrogenation by weakening the Mg–H bond and enabling a sulfur-assisted two-step dehydrogenation mechanism. Experimental results further confirm these theoretical findings. The MgH2/900C–20SO2 sample exhibits that the peak dehydrogenation temperature and the onset dehydrogenation temperature were 19.8 °C and 64 °C lower than that of pure MgH2, and a significant reduction in activation energy from 134.52 kJ mol−1 to 92.12 kJ mol−1. This research provides a comprehensive understanding of the catalytic effects of heteroatom sulfur on MgH2 and offers crucial theoretical and practical insights for the development of more efficient magnesium-based hydrogen storage systems.

Single-Atom Ni Supported on TiO2 for Catalyzing Hydrogen Storage in MgH2.

As an efficient and clean energy carrier, hydrogen is expected to play a key role in future energy systems. However, hydrogen-storage technology must be safe with a high hydrogen-storage density, which is difficult to achieve. MgH2 is a promising solid-state hydrogen-storage material owing to its large hydrogen-storage capacity (7.6 wt %) and excellent reversibility, but its large-scale utilization is restricted by slow hydrogen-desorption kinetics. Although catalysts can improve the hydrogen-storage kinetics of MgH2, they reduce the hydrogen-storage capacity. Single-atom catalysts maximize the atom utilization ratio and the number of interfacial sites to boost the catalytic activity, while easy aggregation at high temperatures limits further application. Herein, we designed a single-atom Ni-loaded TiO2 catalyst with superior thermal stability and catalytic activity. The optimized 15wt%-Ni0.034@TiO2 catalyst reduced the onset dehydrogenation temperature of MgH2 to 200 °C. At 300 °C, the H2 released and absorbed 4.6 wt % within 5 min and 6.53 wt % within 10 s, respectively. The apparent activation energies of MgH2 dehydrogenation and hydrogenation were reduced to 64.35 and 35.17 kJ/mol of H2, respectively. Even after 100 cycles of hydrogenation and dehydrogenation, there was still a capacity retention rate of 97.26%. The superior catalytic effect is attributed to the highly synergistic catalytic activity of single-atom Ni, numerous oxygen vacancies, and multivalent Tix+ in the TiO2 support, in which the single-atom Ni plays the dominant role, accelerating electron transfer between Mg2+ and H- and weakening the Mg-H bonds. This work paves the way for superior hydrogen-storage materials for practical unitization and also extends the application of single-atom catalysis in high-temperature solid-state reactions.

Hydrogen storage properties of MgH2 modified by efficient Co3V2O8 catalyst

Developing medium temperature hydrogen storage materials is important for the practical application of the Studies have demonstrated that V-based catalysts exhibit exceptional catalytic activity in the dehydrogenation of MgH2 at medium levels. However, the V-base catalysts primarily concentrates on hydrogen desorption, and there is a necessity for further enhancement of hydrogen absorption properties. To solve this problem, herein we prepared a bimetallic oxide. Co can enhance the hydrogen absorption and desorption properties of MgH2 as the catalyst and it influences the performance of hydrogen absorption more obviously than the hydrogen desorption performance. It is found that MgH2 catalyzed by Co3V2O8 can absorb 1.31 wt% hydrogen within 30 min even under room temperature and can release 3.41 wt% hydrogen within 120 min at temperatures as low as 225 °C. The activation energy of MgH2-6 wt.%Co3V2O8 is determined to 68.5 kJ/mol, which is 50.2 % lower than that of Ball-MgH2. XRD combined with TEM measurements revealed that the in-situ formed Co and V2O3 can weaken the HH and MgH bonds respectively to improve the hydrogen storage properties of MgH2. These discoveries provide guideline of the further design of high efficiency catalysts for Mg-based hydrogen storage materials.

Microstructure and hydrogen storage properties of MgH2/MIL-101(Cr) composite

In this paper, a new hydrogen storage composite based on magnesium hydride and metal-organic framework MIL-101(Cr) (an acronym for Material Institute Lavoisier) has been mechanically synthesized and investigated. The hydrogen sorption and desorption behavior in the composite was investigated for the temperature and pressure ranges of (593−653) K and (0−3) MPa, respectively. According to the pressure-composition-temperature isotherms of hydrogen sorption/desorption, the MgH2–5 wt%MIL-101(Cr) composite starts to absorb hydrogen at a lower pressure at 593 K. In addition, the hydrogen release peak for composite shifts to lower temperatures by about 140 K compared to the pure milled MgH2 during temperature programmed desorption at a heating rate of 6 K/min. The activation energy of hydrogen desorption from the composite is 120 ± 2 kJ/mol, which is 36% lower than the activation energy of hydrogen desorption from magnesium hydride (189 ± 2 kJ/mol). The enthalpy of hydrogen absorption was found to be 73 kJ/mol H2 and 60 kJ/mol H2 for milled MgH2 and MgH2–5 wt%MIL-101(Cr) composites, respectively. It is showed that the MIL-101(Cr) MOF structures decompose during ball milling and the chromium oxide nanoparticles form a core-shell structure with MgH2 particles. Thus, composite has better sorption and desorption properties than pure magnesium/magnesium hydride due to the nanoconfinement of MgH2. The chromium oxide nanoparticles act as active sites on the surface of the magnesium particles and facilitate the dissociative chemisorption or recombinative desorption of hydrogen. The main regularities of the phase transition in the magnesium-hydrogen system for the composite and magnesium hydride during dehydrogenation have been studied for temperatures in the range of 298–750 K. The in situ analysis of the phase transitions during the dehydrogenation of MgH2 and MgH2–5 wt%MIL-101(Cr) composite indicates a pronounced catalytic effect of the addition of MIL-101(Cr) to the Mg/MgH2. Based on the experimental results and ab initio calculations, a mechanism for the sorption and desorption of hydrogen by the composite has been proposed.

Facile dehydrogenation of MgH2 enabled by γ-graphyne based single-atom catalyst

Solid-state hydrogen storage is a promising roadmap for the safe and efficient utilization of hydrogen energy due to its moderate operating environment and high hydrogen storage density. However, as a representative solid-state hydrogen storage material, magnesium hydride (MgH2) is significantly limited in the commercial application due to its sluggish kinetics in the dehydrogenation process. Single-atom catalysts are a promising solution to this dilemma. However, the promising graphene-based single-atom catalysts are not yet sufficient to meet the dehydrogenation needs in engineering. To further address this dilemma, we designed a novel γ-graphyne based single-atom catalysts including eight 3d transition metals for promoting the dehydrogenation process of MgH2. Through using spin-polarized density functional theory calculations, we found that the energy barrier for MgH2 dehydrogenation has been significantly reduced even to 0.70 eV, which is far lower than the current graphene-based single-atom catalyst. In detail, the migration trajectory of hydrogen atom in the dehydrogenation process has been observed and confirmed using the ab initio molecular dynamics simulations. To investigate the intrinsic origin for its high catalytic activity of single-atom catalyst, we analyze the HMg bond activation mechanism through the electron localization function, charge density difference and crystal orbital Hamiltonian population. Finally, we found the relationship between energy barrier with electronic structure of single-atom catalyst, such as electrostatic potential and system electronegativity. This work can not only provide new ideas for the optimize of dehydrogenation catalyst, but also lay a theoretical foundation for the design of novel energy storage material.

Schottky-structured CoNi-CoO@rGO for accelerating hydrogen storage in magnesium hydride

Herein, a novel approach by designing Schottky-structured CoNi nano-alloys were introduced. After compositing with MgH2, its initial hydrogen absorption started at a low temperature of 40 °C. At a temperature of 300 °C, 6.5 wt% of H2 was released in only 10 min. Furthermore, the kinetic analysis revealed a pivotal transformation in the control model for dehydrogenation of MgH2, shifted from surface penetration to diffusion at a moderate temperature of 250 °C with the introduction of CoNi-CoO@rGO. After modification, the activation energy for hydrogen de/absorption decreased from 116 kJ/mol and 79.39 kJ/mol, to 66 kJ/mol and 54.39 kJ/mol, respectively. It is noteworthy that the CoNi-CoO@rGO-modified MgH2 exhibited excellent cycling performance, retained an impressive hydrogen storage capacity of 97% after 20 cycles at 300 °C. The innovation of this work lies in the following three aspects: 1) the uniform distribution of CoNi-CoO@rGO nanoparticles on the surface of MgH2 significantly enhanced the contact area and promoted the catalytic activity, 2) the synergistic effect between Mg2Co-Mg2CoH5 and Mg2Ni-Mg2NiH4 attenuate the intensity of the Mg-H bond and quickened the post-discharge of MgH2, 3) the incorporation of a CoO-induced Schottky structure accelerated the H transfer in MgH2 and improved the hydrogen absorption and release efficiency.

Endothermic Dehydrogenation-Driven Preventive Magnesiation of Sio by Magnesium Hydride for High-Performance Sio-Based Lithium Storage Materials

Silicon monoxide (SiO)-based materials have gained much attention as high-capacity lithium storage materials because of their superior cycle performance. However, low initial Coulombic efficiency (ICE) of SiO derived from the irreversible electrochemical reaction of the amorphous SiO2 phase in SiO makes wide use of the SiO-based anode materials in lithium-ion batteries challenging. Magnesiation of SiO is one of the promising solutions to improve ICE of SiO-based anode materials. Here, we propose an endothermic dehydrogenation-driven magnesiation of SiO by employing MgH2 to improve both ICE and cycle performance. The resulting Si/Mg2SiO4 nanocomposite material showed much-improved ICE of 89.5% and long-term cycle performance for over 300 cycles compared to the homologue prepared by the magnesiation of SiO using Mg and pristine SiO. High-resolution transmission electron microscopy with thermogravimetry−differential scanning calorimetry revealed that the endothermic dehydrogenation of MgH2 mitigates the rapid temperature rise during magnesiation of SiO, thereby inhibiting the increase of Si domain size in the resulting Si/Mg2SiO4 nanocomposite. Detailed material characterization and electrochemical analysis of Si/Mg2SiO4 nanocomposite materials will be discussed in this presentation.

Ameliorating the re/dehydrogenation behaviour of MgH2 by zinc titanate addition

Magnesium hydride (MgH2) is the most feasible and effective solid-state hydrogen storage material, which has excellent reversibility but initiates decomposing at high temperatures and has slow kinetics performance. Here, zinc titanate (Zn2TiO4) synthesised by the solid-state method was used as an additive to lower the initial temperature for dehydrogenation and enhance the re/dehydrogenation behaviour of MgH2. With the presence of Zn2TiO4, the starting temperature for the dehydrogenation of MgH2 was remarkably lowered to around 290 °C–305 °C. In addition, within 300 s, the MgH2–Zn2TiO4 sample absorbed 5.0 wt.% of H2 and 2.2–3.6 wt.% H2 was liberated from the composite sample in 30 min, which is faster by 22–36 times than as-milled MgH2. The activation energy of the MgH2 for the dehydrogenation process was also downshifted to 105.5 kJ/mol with the addition of Zn2TiO4 indicating a decrease of 22% than as-milled MgH2. The superior behaviour of MgH2 was due to the formation of MgZn2, MgO and MgTiO3, which are responsible for ameliorating the re/dehydrogenation behaviour of MgH2. These findings provide a new understanding of the hydrogen storage behaviour of the catalysed-MgH2 system.

The phase transitions behavior and defect structure evolution in magnesium hydride/single-walled carbon nanotubes composite at hydrogen sorption-desorption processes

The development of hydrogen storage methods is one of the important areas of research in the field of hydrogen energy, while metal hydrides and composites based on them are the most preferred candidates for this. In this paper, one of the composite hydrogen storage materials based on magnesium hydride and single-walled carbon nanotubes was considered. The hydrogen sorption and desorption behavior in composite have been investigated for temperatures and pressures ranges (593−653) K and (0−3) MPa, respectively. Using scanning electron microscopy, it was shown that carbon nanotubes are homogeneously distributed on the surface of MgH2 particles and some of nanotubes are partially embedded in the bulk of MgH2. According to pressure-composition-temperature curves and Van’t Hoff plots it was determined that the enthalpy value of hydrogen absorption process was 69 KJ/mol H2 and 62 KJ/mol H2 for milled MgH2 and MgH2 with 5 wt% single-walled carbon nanotubes, respectively. The main regularities of phase transition in the magnesium-hydrogen system for composite and magnesium hydride during dehydrogenation have been researched for temperatures in the range of 298–750 K. The in situ analysis of the phase transitions during dehydrogenation of MgH2 and composite based on MgH2 and 5 wt% of single-walled carbon nanotubes in argon atmosphere indicates pronounced catalytic effect of carbon nanotubes on the hydrogen desorption. The thermally stimulated desorption curves showed that hydrogen begins to release from the composite where the MgH2 decomposition is minimal. An in situ Doppler broadening spectroscopy study revealed that this is caused by a significant changes magnesium defect structure as a result of the carbon nanotubes/nanoparticles embedding, and the low-temperature hydrogen release follows from the decomposition of associated defects (dislocation-hydrogen or vacancy-hydrogen complexes) as well as its effective diffusion to the surface.

Enhanced hydrogen properties of MgH2 by Fe nanoparticles loaded hollow carbon spheres

In the present investigation, we have reported the synergistic effect of Fe nanoparticles and hollow carbon spheres composite on the hydrogen storage properties of MgH2. The onset desorption temperature for MgH2 catalyzed with hollow carbon spheres and Fe nanoparticle (MgH2-Fe-HCS) system has been observed to be 225.9 °C with a hydrogen storage capacity of 5.60 wt %. It could be able to absorb 5.60 wt % hydrogen within 55 s and desorb 5.50 wt % hydrogen within 12 min under 20 atm H2 pressure at 300 °C. The desorption activation energy of MgH2-Fe-HCS has been found to be 84.9 kJ/mol, whereas the desorption activation energies for as received MgH2, Hollow carbon sphere catalyzed MgH2 and Fe catalyzed MgH2 are found to be 130 kJ/mol, 103 kJ/mol, and 94.2 kJ/mol respectively. MgH2-Fe-HCS composite lowered the change in enthalpy of hydrogen desorption from MgH2 by 20.02 kJ/mol as compared to pristine MgH2. MgH2-Fe-HCS shows better cyclability up to 24 cycles of hydrogenation and dehydrogenation of MgH2. The mechanism for the better catalytic action of Fe and HCS on MgH2 has also been discussed.

Hydrogen release mechanisms of MgH2 over NiN4-embedded graphene nanosheet: First-principles calculations

In this study, first-principles calculations were performed to investigate the catalytic effect of NiN4-G on the dehydrogenation of MgH2. Side-on MgH2 can be adsorbed stably on the NiN4-G monolayer and is preferentially adsorbed on the NiN4 site compared with the graphene site. The hydrogen desorption process, in which MgH2 dissociated to the Mg atom on the NiN4 site or graphene site and an H2 molecule in the vacuum, should overcome lower barriers than pure MgH2. This is because the corresponding Mg–H bond is weakened owing to the electron transfer between the Mg atom and the substrate. The hydrogen desorption enthalpies of the (MgH2)5 cluster on the NiN4 active and graphene sites are significantly smaller (0.11 eV and 1.50 eV, respectively) when H2+H2 is released from the cluster compared with those of the undoped MgH2 cluster (2.48 eV). Therefore, the NiN4-G monolayer can provide the double effect of the NiN4 active and graphene sites on improving the dehydrogenation performance of MgH2.

Endothermic Dehydrogenation-Driven Preventive Magnesiation of SiO for High-Performance Lithium Storage Materials.

Silicon monoxide (SiO)-based materials have gained much attention as high-capacity lithium storage materials based on their high capacity and stable capacity retention. However, low initial Coulombic efficiency associated with the irreversible electrochemical reaction of the amorphous SiO2 phase in SiO inhibits the wide usage of SiO-based anode materials for lithium-ion batteries. Magnesiation of SiO is one of the most promising solutions to improve the initial efficiency of SiO-based anode materials. Herein, we demonstrate that endothermic dehydrogenation-driven magnesiation of SiO employing MgH2 enhanced the initial Coulombic efficiency of 89.5% with much improved long-term cycle performance over 300 cycles compared to the homologue prepared by magnesiation of SiO with Mg and pristine SiO. High-resolution transmission electron microscopy with thermogravimetry-differential scanning calorimetry revealed that the endothermic dehydrogenation of MgH2 suppressed the sudden temperature rise during magnesiation of SiO, thereby inhibiting the coarsening of the active Si phase in the resulting Si/Mg2SiO4 nanocomposite.

Achieve high-efficiency hydrogen storage of MgH2 catalyzed by nanosheets CoMoO4 and rGO

The development of high-efficiency carbon-based multifunctional catalysts is of great significance for improving solid-state hydrogen storage materials . Herein, it was confirmed that CoMoO 4 sheet-like nanocatalysts uniformly supported on the surface of reduced graphene oxide (CoMoO 4 /rGO) were successfully prepared by a simple hydrothermal reaction . The novel CoMoO 4 /rGO catalyst was subsequently doped into MgH 2 to improve its hydrogen storage performance. MgH 2 –10 wt% CoMoO 4 /rGO starts to release hydrogen at around 204 °C, which is about 36 °C and 156 °C lower than that of MgH 2 −10 wt%CoMoO 4 and pure MgH 2 , respectively. In addition, 6.25 wt% H 2 can be released within 10 min at 300 °C. After complete dehydrogenation , H 2 can be absorbed below 80 °C. Meanwhile, it can absorb 4.2 wt% H 2 in 20 min under the condition of 150 °C and 3 MPa. Moreover, the activation energy of hydrogen absorption and dehydrogenation of MgH 2 –10 wt%CoMoO 4 /rGO composites are reduced by 31.44 kJ mol −1 and 33.78 kJ mol −1 , respectively, compared with pure MgH 2 . Cycling experiment shows that the MgH 2 –10 wt%CoMoO 4 /rGO composite system can still maintain about 98% of the hydrogen storage capacity after 10 cycles. Furthermore, studies on the catalytic mechanism show that the synergistic effect between the in-situ generated MgO, Co 7 Mo 6 and Mo may help to promote the diffusion of H 2 , thereby improving the MgH 2 Hydrogen storage properties. • MgH 2 –10 wt%CoMoO 4 /rGO composite system was reported for the first time. • MgH 2 –10 wt%CoMoO 4 /rGO composite material starts dehydrogenation at about 204 °C. • MgH 2 –CoMoO 4 /rGO composites showed promising kinetic properties. • MgH 2 –CoMoO 4 /rGO composites showed good cyclic stability. • MgO, Mo and Co 7 Mo 6 were formed in situ during the reaction.

Catalytic role of binary oxides (CuO and Al2O3) on hydrogen storage in MgH2

AbstractHydrogen sorption characteristics of magnesium hydride (MgH2) were enhanced by ball milling for 12 h under an inert atmosphere with the addition of 20 wt% Al2O3 and as prepared CuO. X‐ray diffraction (XRD) characterization and thermal gravimetric analyzer coupled with a mass spectrometer (TGA‐MS) of the ball milled samples were carried out to determine the H2 sorption reactions. Additionally, XRD data were analyzed using Rietveld method to identify the crystallographic properties. Ball milled MgH2 with β and γ allotrope mixtures were found with broad peaks in XRD indicating the as prepared samples are amorphous and strain, alongside bare additives. H2 sorption in MgH2 is greatly enhanced by the presence of CuO and Al2O3 binary oxides. TGA experiment demonstrated fast desorption kinetics for ball milled samples with the oxide additives. Particularly, MgH2 milled with CuO showed a more remarkable effect on desorption kinetics rather than Al2O3. It takes less than 10 min to desorb more than 5 wt% H2 at 623 K. The activation energy of H2 desorption was estimated for the mixtures by Kissinger method and the lowest value (65 kJ mol−1) was obtained for the MgH2/CuO mixture. A kinetic model has been proposed in the context to illustrate the complex mechanism of dehydrogenation of MgH2 with the additives. Finally, the addition of metal oxides influences H2 sorption characteristics of MgH2 through lowering the activation energy and reducing the waste of energy for diffusing the thin layer of Mg that creates a pathway to store H2 within the system.

Elucidating Evidence for the In Situ Reduction of Graphene Oxide by Magnesium Hydride and the Consequence of Reduction on Hydrogen Storage

The current study highlights important information regarding how graphene oxide (GO) additive interacts with magnesium hydride (MgH2) and transforms to reduced graphene oxide (rGO). A mild reduction occurs during mechanical milling itself, whereas a strong reduction of GO happens concurrently with the oxidation of Mg formed during the dehydrogenation of MgH2. Owing to the in situ transformation of GO to rGO, the dehydrogenation temperature of MgH2 reduces by about 60 °C, whereas the hydrogen ab/desorption reaction kinetics of MgH2 increases by two orders of magnitude and the dehydrogenation activation energy decreases by about 20 kJ/mol. We have thoroughly scrutinized the transformation of GO to rGO by differential scanning calorimetry (DSC), X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM) techniques. Interestingly, the GO to rGO transformation triggered by magnesium hydride in the current study further paves the way for the facile preparation of rGO- and MgO-decked rGO composites, which are important materials for energy storage applications.